The present invention relates generally to photographic printers and more specifically to a filter apparatus for use in a photographic printer which permits the selective positioning of a scanning or large area transmissive filter between a negative and a single light sensor.
In the process of developing photographic negatives, printing the negatives, and developing the prints, it is necessary to measure various density characteristics of both negatives and prints. For example, to monitor the quality of a film processor, it is necessary to measure the transmissive characteristics of a developed strip of transmissive test patches, commonly referred to as a film process control strip. To properly control exposure when printing negatives, it is common practice to scan the transmissive characteristics of each negative at a plurality of discrete locations whereby to measure the scanned transmissive density of each negative. To monitor the quality of a paper processor, it is necessary to measure the reflective density of a developed strip of reflective patches, commonly referred to as a paper process control strip.
Making these various types of densitometric measurements requires the use of different filters. More specifically, measuring the scanned density of a transmissive pictorial negative typically requires the scanning of many small, transmissive scanning filters between the negative and a light sensor. Scanning a pictorial color negative may require, for example, twelve (12) each of red, green, and blue scanning filter. Measuring the large area reflective or transmissive densities of reflective or transmissive color patches requires at least one each red, green, and blue large area transmissive filters.
It is known in the art to provide photographic printers including rotatable discs supporting the required plurality of scanning filters of necessary color (i.e. passband). These discs are rotated between the negative and a light sensor to measure the transmissive characteristics of the negative. These transmissive characteristics are subsequently used to calculate the scanned densities at a plurality of discrete regions on the negative. Such discs, however, make no provisions for the large area transmissive filters required to measure large area transmissive densities.
U.S. Pat. No. 3,229,574 to Neale et al. shows a filter wheel including red, green, and blue large area transmissive filters. The wheel is controlled so as to selectively position each of the filters between the negative and a light sensor, whereby to measure the large area transmissive characteristics of the negatives. These large area transmissive characteristics are subsequently used to calculate the large area transmissive densities of the negatives. Neale et al., however, makes no provisions for measuring the scanned density of the negative.
In the prior art it is thus necessary to provide substantially separate filter positioning and control apparatus for measuring scanned and large area characteristics of negatives or test patches. Further, because such apparatus is separate, two or more photocells are often required, one being associated with the apparatus for measuring the scanned transmissive characteristics, and one being associated with the apparatus used to measure the large area characteristics.